American research team noted for their studies of human sexuality (sexual behaviour, human). William H. Masters (in full William Howell Masters; b. Dec. 27, 1915, Cleveland, Ohio, U.S.—d. Feb. 16, 2001, Tucson, Ariz.), a physician, and Virginia E. Johnson (née Virginia Eshelman; b. Feb. 11, 1925, Springfield, Mo., U.S.), a psychologist, were codirectors of the Masters & Johnson Institute (1973–94).

Masters was educated at Hamilton College in Clinton, N.Y. (B.S.), and the School of Medicine and Dentistry of the University of Rochester (M.D., 1943). In 1947 he joined the faculty of the School of Medicine of Washington University in St. Louis. Johnson studied at Drury College (Springfield, Mo.), the University of Missouri, Columbia, and the Kansas City Conservatory of Music, though she never earned a degree (she later received two honorary D.Sc. degrees). Johnson began work with Masters as a research associate in 1957, assisting him in the sex research that he had begun in 1954. In 1964 they established the Reproductive Biology Research Foundation in St. Louis, Mo., he becoming its director and she later (1973) becoming its codirector. In 1973 they became codirectors of the Masters & Johnson Institute, also in St. Louis. They were married in 1971 and continued to collaborate after their divorce in 1993.

Their book Human Sexual Response (1966) was considered by many to be the first comprehensive study of the physiology and anatomy of human sexual activity under laboratory conditions—much of it the result of actual research observation. Biochemical equipment, such as electrocardiographs and electroencephalographs, was used in recording sexual stimulations and reactions. Though written in arcane language, the book was a best-seller and helped change people's attitudes toward sex. The two also conducted much clinical marriage counseling, dealing with problems of sexual performance. A second important study, Human Sexual Inadequacy, appeared in 1970. Homosexuality in Perspective, a report on the clinical treatment of the sexual problems of homosexuals, was published in 1979. Other works, cowritten with Robert C. Kolodny, include Human Sexuality (1982), Crisis: Heterosexual Behaviour in the Age of AIDS (1988), and Heterosexuality (1994). With Masters's retirement in 1994, the Masters & Johnson Institute closed.